At present, the United States holds large and available natural gas, propane, and other gaseous fuel resources. These types of fuel are particularly attractive due, in part, to the significantly reduced emissions that gaseous fuel engines produce relative to those of liquid fuel engines. Gaseous fuel automotive engines, therefore, present an attractive option for automotive vehicles. If appropriate technology existed to effectively and efficiently use gaseous fuels, then a much wider variety of fuel options could be available to power automotive engines. Most known automotive engine technology for improved engine performance, however, applies to liquid fuel systems.
One broad technological area in which automotive gaseous fuel engines need substantial improvement is in fuel metering, i.e., the technology of precisely controlling the flow rate of fuel to the engines. Specific areas of fuel metering technology in which needs exist include (1) increasing the dynamic range of the gaseous fuel flow; (2) compensating for temperature changes in the gaseous fuel; (3) compensating for fuel composition changes in gaseous fuels; and (4) compensating for a phenomenon known as "regulator droop" as the fuel flows to the gaseous fuel engine.
The problem of fuel flow dynamic range may be seen in the example of one commercially-available automobile engine that uses compressed natural gas. That engine suffers in fuel metering performance at both ends of its metering dynamic range. At the low end of the dynamic range, i.e., when delivering small amounts of fuel to the engine, fuel system performance is unstable. This, in turn, makes engine performance unstable. At the other end of the dynamic range, the amount of gaseous fuel that the system can deliver to the engine is limited. Since the amount of gaseous fuel to the engine is limited, the power that the engine produces is also limited. Consequently, existing gaseous fuel engines of this type are less stable when idling and have lower peak torque and power at maximum speed than their liquid fuel counterparts
Compensating for temperature changes is of particular importance in engine systems that have been converted, either as part of their manufactured design or in the automotive aftermarket, to use compressed natural gas or other gaseous fuels. These OEM engine systems require temperature compensation because their performance may vary drastically depending on whether the gaseous fuel is hot or cold. No known method or system permits this type of compensation for the purpose of improved fuel metering and system performance in a gaseous fuel engine system that was not originally designed with temperature compensation capability.
The composition of gaseous fuels is known to vary significantly around the United States. In "The Impact of Natural Gas Composition on Fuel Metering and Engine Operational Characteristics," International Congress & Exposition, Detroit, Mich., Feb. 24-28, 1992, Soc. of Automotive Eng'rs, Paper No. 920593 by Steven R. King, one of the present co-inventors, appears an explanation of the effects of gaseous fuel composition on gaseous fuel engines. At present, no known method or system exists that compensates for these variations in gaseous fuel properties
The phenomenon known as "regular droop" poses yet another area of gaseous fuel metering technology in which significant limitations currently exist. Regulator droop may be characterized as a drop in fuel outlet pressure that occurs in a regulator as the gaseous fuel flow rate increases. At low flow rates, most regulators comfortably maintain a constant gaseous fuel outlet pressure. As flow rates increase, however, fuel outlet pressure becomes increasingly difficult to maintain due to mechanical design limitations within the regulator. This effect limits the operation of the gaseous fuel engine by reducing the quantity of fuel that can be supplied to the engine. No method or system, however, exists to solve this problem.
Since no method or system exists to separately solve any of the above problems, none exists to solve any combination of them. Moreover, for efficient operation of an automotive gaseous fuel engine, it is important that engine designers have solutions to the majority, and preferably all, of these limitations.
Consequently, there is a need for a gaseous fuel delivery method and system that provides to a gaseous fuel engine a wide dynamic range of fuel flow. Such a method and system for metering gaseous fuel to gaseous fuel engines would improve engine stability at low engine speeds and allow more fuel to reach the engine to thereby increase maximum engine power.
There is a need for an improved fuel metering method and system that compensates for temperature changes in the gaseous fuel as it flows to the gaseous fuel engine.
There is a further need for a method and system that determines and compensates for fuel composition variations in gaseous fuel so as to generally improve the performance of the gaseous fuel engine.
There is yet a need for a fuel metering method and system that avoids regulator droop as gaseous fuel flows to the gaseous fuel engine.